This invention relates to a disc reproducing device in which, when it is difficult to utilize synchronizing signals recorded on a disc, the speed of rotation of the disc is maintained approximately at a predetermined value.
When a video disc data reading device scans a scratch on a disc surface, or when the tracking servo or focus servo is unlocked, it is sometimes substantially impossible to read data from the disc and no reproduction signal is outputted. As a result, the demodulation output includes noise and the separated horizontal synchronizing signal does not have correct time base information, whereby the phase comparator which produces a time base error signal is operated erroneously. When the data reading position on the disc is scanned across the data tracks, the same disadvantages tend to occur. Therefore, the spindle servo unit is operated irregularly and the rotating speed of the spindle motor, i.e., the rotating speed of the disc, is deviated from its normal value. The worst case of this could lead to running of the disc at extremely high speed with consequent damage to the device.
Even if it is recovered from such a state, it is still difficult to produce correct time base information from the horizontal synchronizing signal because of the effects of demodulation output noise on the speed of rotation vs. demodulation amplitude output characteristic of the demodulation circuit and the time constant of the horizontal synchronizing separator circuit. Accordingly, it is difficult to lock the spindle servo in a short time.